This invention relates to a method and apparatus for providing a known color standard or reference within film areas within or directly adjacent to exposed frames along a roll of photographic film. The color standard is subsequently usable in the analysis of color values portrayed in the individual frames. The color standard areas are exposed under known conditions simultaneously with exposure of the corresponding film frames. Since the paired areas of film will be subjected to the same handling and development procedures, deviations from the preselected color standard values are measurable to provide an absolute reference against which the corresponding values in the exposed film frames can be compared.
This invention arose from an effort to further refine and perfect the methods disclosed in U.S. Pat. No. 4,227,211. The patent, which is hereby incorporated into this disclosure by reference, discloses a method for analyzing crop growing conditions during a growing season. The method involves aerial photographing of the crop and color analysis of the resulting photographs. In order to provide accurate comparison between photographs taken at different times of the day, on different days, and under different lighting conditions, and also to compensate for differing handling and developing of various rolls of film, it is essential to provide a color standard or reference against which each frame can be compared.
In the method as disclosed in Patent No. 4,227,211, the reference standard is achieved by exposing a frame of the film under known artificial light conditions to portray colored panels by reflective light. This has been found to be generally satisfactory when using hand-held cameras and relatively short rolls of film.
The use of a single slide or frame as a reference or standard for an entire roll of film is impractical when applying the crop analysis method to larger scale aerial cameras. These cameras typically use much longer rolls of film, which might be exposed over a substantial period of time. Since ambient lighting conditions vary over that period, and since film tends to "age" during handling and developing, there can exist substantial variations in the photographed images from one end of the long roll of film to the other. It is therefore necessary to provide multiple color standards along the length of the roll of film, and most preferable to provide a color standard in conjunction with each exposed film frame.
Furthermore, it is desirable to modify the color standard for different types of crops or vegetation being photographed along a single roll of film. By selecting a color standard including individual color components expected in the vegetation as portrayed in the area being photographed, one can draw immediate emperical comparisons between the actual photographs and the known standard. Modifying wall mounted color charts or areas is relatively difficult, very cumbersome, and basically impractical.
Color references associated with individual film frames have been previously proposed with respect to printing methods. An example is illustrated by U.S. Pat. No. 4,211,558 to Oguchi et al, issued July 8, 1980. A method is disclosed which involves printing a color or light sample of the ambient light average in the field of view of the sample receptor adjacent to each film frame, so that comparisons can be made to the color in the frame for accurate printing. The color sample is exposed simultaneously with the film frame, and records the light illuminating the object being photographed. This provides a reference for exposure correction purposes.
According to the present invention, an absolute color reference is desired, rather than the relative reference which would be attained by use of the ambient light illuminating the object being photographed. The present method and apparatus provide known color values to expose an area of film adjacent to the film frame by transmission of repeatable light values from a light source through variable filters selected to match expected color components in the vegetation portrayed in the land area being photographed.
It is an object of this invention to provide a method and apparatus whereby each film frame will be accompanied by a known color standard imprinted within or immediately adjacent to it and subjected to the same handling and developing sequences. Accurate correction factors and color comparisons can then be utilized in the analysis of the color values in the film frame itself.